The present invention relates, generally, to the chemical mechanical planarization of a workpiece and, more particularly, to the chemical mechanical planarization of a workpiece using a homogeneous fixed abrasive polishing pad.
A chemical mechanical planarization (CMP) process is widely used in the manufacturing process of VLSI devices with sub-micron geometries. The CMP process reduces the step height between the high and low features on the surface of a semiconductor wafer allowing subsequent lithography steps to operate on a planar surface. This allows for multiple layers of deposition on the wafer and allows for the creation of semiconductor devices with greater feature densities.
More particularly, a resinous polishing pad having a cellular structure is traditionally employed in conjunction with slurry, for example, a water-based slurry comprising colloidal silica particles. When pressure is applied between the polishing pad and the workpiece (e.g., silicon wafer) being polished, mechanical stresses are concentrated on the exposed edges of the adjoining cells in the cellular pad. Abrasive particles within the slurry concentrated on these edges tend to create zones of localized stress at the workpiece in the vicinity of the exposed cell edges. This localized pressure creates mechanical strain on the chemical bonds comprising the surface being polished, rendering the chemical bonds more susceptible to chemical attack or corrosion (e.g., stress corrosion). Consequently, microscopic regions are removed from the surface being polished, enhancing planarity of the polished surface. See for example, Arai et al., U.S. Pat. No. 5,099,614, issued March 1992; Karlsrud, U.S. Pat. No. 5,498,196, issued March 1996; Arai et al., U.S. Pat. No. 5,329,732, issued July 1994; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March 1996, for further discussion of presently known lapping and planarization techniques. By this reference, the entire disclosures of the foregoing patents are hereby incorporated by reference herein.
As the size of microelectronic structures used in integrated circuits decreases to sub-half-micron levels, and as the number of microelectronic structures on current and future generation integrated circuits increases, the degree of planarity required increases dramatically. The high degree of accuracy of current lithographic techniques for smaller devices requires increasingly flatter surfaces. However, presently known polishing techniques are believed to be inadequate to produce the degree of local planarity and global uniformity across the relatively large surfaces of silicon wafers used in integrated circuits, particularly for future generations.
A typical CMP process used to manufacture VLSI devices involves polishing built-up layers of dielectrics and conductors used to form integrated chips on a wafer. The wafer is pressed against a compliant polishing pad in the presence of a slurry containing suspended abrasive particles. High features on the surface of the wafer cause high-pressure areas against the polishing pad that result in an increased removal rate in the area of the high feature. In a similar manner, low features cause low-pressure areas against the polishing pad that result in a decreased removal rate in the area of the low features. The combination of increased removal at areas having high features and decreased removal at areas having low features improves the planarity of the surface of the wafer.
However, the compliant nature of conventional polymeric polishing pads allows the polishing pad to also remove material, albeit at a slower rate, in areas having low features. In addition, the abrasives in the slurry are able to collect in the low feature areas undesirably increasing the removal rate in the low feature areas. Even though the removal rates from the low areas is lower than the removal rates in the higher areas, the difference in the removal rates, or selectivity to topography, is not sufficient.
A need therefore exists for a polishing pad that has greater selectivity to topography to improve the planarity of the workpiece during a chemical mechanical planarization process. In addition, a manufacturing method is needed to produce the improved polishing pad.
These and other aspects of the present invention will become more apparent to those skilled in the art from the following non-limiting detailed description of preferred embodiments of the invention taken with reference to the accompanying figures.
In accordance with an exemplary embodiment of the present invention, a homogeneous fixed abrasive polishing article, or pad, includes a cured resin coated talc matrix having at least one working surface and an abrasive uniformly distributed throughout the cured resin coated talc. In a preferred embodiment, the abrasive comprises ceria.
In accordance with another exemplary embodiment of the of the present invention, a homogeneous fixed abrasive polishing pad includes a filler material having a hardness less than 3 on the Mohs hardness scale. An abrasive is uniformly distributed throughout the filler material and a plurality of conduits is created through the filler material for delivering a fluid through a polishing pad.
In accordance with yet another exemplary embodiment of the present invention, a homogeneous fixed abrasive polishing pad includes a filler material having a hardness less than 3 on the Mohs hardness scale wherein the filler material has at least one substantially planar working surface. An abrasive is uniformly distributed throughout the filler material and a plurality of grooves is created in the working surface for the transportation of fluids over the working surface.
In accordance with yet another exemplary embodiment of the present invention, a method for manufacturing a homogeneous fixed abrasive polishing pad having a working surface is provided. The method includes the steps of mixing a binder, a solvent and a filler material together, wherein the filler material has a hardness less than 3 on the Mohs hardness scale, thereby creating a resin coated filler material. Drying the resin coated filler material. Grinding the resin coated filler material. Sieving the resin coated filler material. Mixing an abrasive material with the resin coated filler material. Sieving the abrasive material and the resin coated filler material thereby creating a powder material.
Transferring the powder material to a mold wherein the mold has at least one substantially planar surface to form a working surface for the polishing pad. Compressing the powder material. Curing the powder material, preferably in an oven. Removing the cured powder material from the mold and preparing the cured powder material for use on a chemical mechanical planarization tool. In a preferred embodiment, conduits through the polishing pad and/or grooves on the working surface of the polishing pad are created. In addition, one or more optically transparent windows or plugs may be formed in the polishing pad. The windows may be of a suitable polymer material for facilitating optical inspection of a workpiece through the transparent window.
In accordance with yet another exemplary embodiment of the present invention, another method for manufacturing a homogeneous fixed abrasive polishing pad having a working surface is provided. The method includes the steps of mixing a binder, a solvent, an abrasive material and a filler material together, wherein the filler material has a hardness less than 3 on the Mohs hardness scale, thereby creating a resin coated abrasive-filler material. Drying the resin coated abrasive-filler material. Grinding the resin coated abrasive-filler material. Sieving the resin coated abrasive-filler material thereby creating a powder material. Transferring the powder material to a mold. Compressing the powder material within the mold. Curing the powder material, preferably by heat. Removing the cured powder material from the mold and preparing the cured powder material for use on a chemical mechanical planarization tool.